1. Technical Field
The present invention, involving adhesive applicators associated with bookbinders and bookbinders employing adhesive applicators, relates to improvements in adhesive application mechanisms for applying hot-melt adhesive to the spine-portion endface of sheet bundles collated into block form.
2. Description of the Related Art
Generally, this kind of adhesive application device is widely known to collate into a bundle shape sheets conveyed from an image-forming apparatus or the like and hold that bundle at a predetermined adhesive application position. It is equipped with an adhesive container that applies adhesive to a bottom edge of the sheet bundle (the spine binding portion) and to coat an adhesive roller disposed in this container with adhesive for application. A method is also widely used to store hot-melt adhesive in the adhesive container and to melt it with heating means.
For example, a device that has an adhesive container below the sheet bundle held in an upright posture and applies a predetermined amount of adhesive using an applicator roller while moving this container along the spine binding edge of the sheet bundle is proposed in Japanese Unexamined Pat. App. Pub. No. 2007-76118. In this publication, a refilling mechanism that supplies solid-form adhesive to the container and a device that is equipped with heating means to melt the solid-form adhesive charged into this container.
It is necessary to refill the adhesive when the system is designed to store hot-melt adhesive in the container and to use heat to melt the adhesive for application. The container is configured to be large. To refill a large amount of adhesive at one time, there is the problem that it takes a long time to melt the charged adhesive. This problem causes the dropping of the adhesive temperature which can cause the adhesive in the container to harden or becoming semi-hardened (gel-form) when the machine is not being used or between applications of adhesive.
Here, Pat. App. Pub. No. 2007-76118 proposes a comparatively small and compact container that stores the adhesive and a device that supplied the adhesive according to the status of adhesive consumption in the device. In this publication, a refilling mechanism has a sensor to detect the amount of adhesive in the container and supply a predetermined amount of solid-form adhesive to the container according to detection signals from this sensor.
Conventionally, regardless of the volume of the adhesive container, this sensor detects that the adhesive in the container has been consumed below a predetermined level. The system is configured to charge a preset amount (fixed amount) of adhesive at the detection signals from this sensor. Normally, this sensor detects a state (near-empty) just prior to the adhesive in the container becoming empty. After the adhesive application in the finishing process is ended, adhesive is charged into the container for the next adhesive application process.
As described above, a sensor (level sensor) is provided to detect the amount of adhesive in the adhesive container, and when refilling adhesive at a signal, conventionally, the sensor detects a near-empty state and after the detection, and the predetermined application operation (finishing operation) is ended, a predetermined amount of adhesive is charged into the container.
In such a case, if the container is configured to be large, the amount of adhesive to refill is higher and melting requires more time. Also, if the container is configured to be compact, the melting time is shorter, but the adhesive must be refilled more frequently.
Meanwhile, the amount of adhesive consumed greatly varies depending on the size and thickness of the sheet bundle to be coated with adhesive. For example, when the bookbinding device binds a maximum size of 100 sheets in the sheet bundle, the amount of adhesive consumed for 10 sheets 1/10 the total amount. Even if the number of copies to be coated with adhesive consecutively cannot be determined uniformly because there are times when there are 10 copies, or when there are as many as 100 copies.
Conventionally, the refilling of adhesive to the container was set in the following way. First, the maximum and minimum levels of adhesive in the container were set when the unit is designed. Then, when a sensor that detects when the adhesive amount has reached the minimum level, the application operation is set to be completed when it detects a near-empty state. In other words, the adhesive amount when in a near-empty state is set to be able to apply adhesive at least one time when the sheet bundle is a maximum size, and the thickness is the maximum sheet bundle thickness. The system is set so that the refilling amount of adhesive to the container is the maximum level when the adhesive in the container is consumed to the minimum level so that the adhesive does not exceed the maximum level and overflow the container.
In this way, the following problems were created with the conventional adhesive refilling method. When the near-empty sensor has detected that the adhesive is at a minimum level, the adhesive amount control means refills a predetermined amount of adhesive to the container and sets it to the maximum level of the container when the process to apply adhesive to the sheet bundle being coated part way is ended. For that reason, the system must wait until the adhesive reaches a predetermined temperature to continue applying adhesive to subsequent sheet bundles. However, even though the amount of adhesive remaining in the container is adequate if the subsequent sheet bundle is a low number of copies, for example one sheet bundle, the system is interrupted to refill the adhesive.
If the maximum sheet bundle thickness for that unit is 100 sheets, and the system is set to be able to apply adhesive for 100 sheets after the near-empty state is detected, and the actual sheet bundle is 10 sheets, it is possible to continue applying adhesive to 10 sheet bundles with the amount of adhesive remaining in the container. In such a case, when the number of sheet bundles to be subsequently processed is less than 10 copies, even though it is possible to continue applying adhesive, the system is interrupted to refill the adhesive.
Also, when the sensor detects a near-empty state, even if the subsequent number of sheet bundles is low, conventionally, a predetermined amount of adhesive is refilled to reach the maximum level. Therefore, even if the insufficient adhesive is enough for one sheet bundle, a predetermined amount of adhesive is refilled, so there is the problem of requiring a longer amount of waiting time to refill the adhesive (melting time when using hot-melt adhesive).
This problem occurs frequently if the size of the container is smaller, and if the container is larger, the frequency of the problem is lower, but the time required to wait for the refilling of adhesive is longer. Even if the container is configured to be large or small, the conventional method to refill adhesive has the problem of an unnecessarily long wait for processing because adhesive is refilled until the maximum level regardless of the number of sheet bundles, the size and the bundle thickness when the sensor has detected a near-empty state.